1. Field of the Invention
The present invention relates to a method of PLMN selection in multi-network environment and to a mobile radio communications device arranged for operation in such an environment.
2. Description of the Related Art
It has become increasingly common for mobile radio communications device User Equipment (UE) to achieve connection with one of a plurality of possible networks in particular to achieve continuity of service even where the Home Public Land Mobile Network (HPLMN) with which the UE is normally registered might not be (temporarily) available.
There are also various operational scenarios in which initial connection to the HPLMN might not arise and wherein the UE remains registered with the most recent Registered Public Land Mobile Network (RPLMN) even though the HPLMN, or any other higher priority PLMN, might be available and might offer a preferred connection.
With regard to the various specification proposals arising in accordance with Release 63rd Generation Partnership Project (3GPP), the UE will always attempt to register with the last RPLMN at the time of Power-On or at the time of recovery from an out-of-service period. It has been proposed however in Release 7 3GPP specifications that a user, or network operator, can establish an option in the Subscriber Identity Module (SIM) in order to permit the UE to register with its HPLMN when available during a Power-On, or service recovery scenario.
However, such proposals take no account of the actual use of UE within a network-sharing scenario, and importantly, in scenarios whereby a UE is likely to move between different cells, generally belonging to different Location Areas, which do not offer connection to the same selection of networks.
As noted with the availability of a plurality of potential networks for connection via a UE, more than one operator can effectively share the same physical network. On this basis, the identities of all available PLMNs (via operator services) in a particular cell are transmitted to the UEs within the standard system information.
In a shared network environment, all of the cells belonging to one Location Area are arranged to offer the services of the same set of available operators. However, cells belonging to different Location Areas can offer a different selection of network operators and of course it is quite likely that a UE will move between the respective cells of such different Location Areas.
The present invention is related in particular to a scenario in which a HPLMN for a UE is available in one Location Area but not in one or more other such areas.
Currently, if a UE is registered with a RPLMN and moves into a new Location Area, no initial check for its HPLMN is conducted although some form of location update signaling is performed and in accordance in particular with 3 GPP TS 23.122 subclause 4.4.3. Here it is stated that when the mobile station reselects to a cell of a shared network, the access system may indicate multiple PLMN identities to the non-access stratum although the mobile station can choose from such multiple PLMNs, if the RPLMN is available among such multiple PLMNs, the mobile station shall not choose a different PLMN.
Although, upon moving to the new Location Area, the UE performs the aforementioned location update, it can also be arranged to perform periodic searches for its HPLMN. If, in accordance with such searches the HPLMN is located, the UE will reselect to its HPLMN.
Such periodic searching is controlled by way of a HPLMN search timer which is known to operate in accordance with a variety of different and ever increasing timer periods generally in the magnitude of minutes. Also, in some scenarios, this timer is disabled so as to save battery power and in these instances, there is no way of achieving reselection to the HPLMN while the RPLMN remains available.
The aforementioned scenario applies equally where a more desirable, but not necessarily on HPLMN, might be available such as a higher priority PLMN.
Such known operational scenarios exhibit certain disadvantages.
Upon moving into a new location area, the UE initially performs location area update with the RPLMN and, subsequently, performs registration with the HPLMN or any other high priority PLMN assuming that the HPLMN search time has not been disabled. This leads to a disadvantageous repeated signaling between the network and the UE.
Also, the UE remains registered with the “non-home” or “visited” PLMN until expiry of the HPLMN search timer which can lead to service delays and inefficiencies. It will further also not prove cost-effective for both the user and network operator.